DD 01Technical Data

Dowel Systems

The importance of eliminating vertical joint movement

DIAMOND DOWELFOR SLABS ON THE GROUND

VIPER DOWEL FOR SUSPENDED SLABS AND JOINTLESS FLOORS

SUPERSLEEVESQUARE DOWEL BAR AND SLEEVE SYSTEM

TRI-PLATESAW-CUT CONTRACTION JOINTS

BETTER SOLUTIONS FOR CONCRETE FLOORS

Dowel Systems DD 01Technical Data

THE IMPORTANCE OF ELIMINATING VERTICAL JOINT MOVEMENT AND ALLOWING TWO WAY LATERAL MOVEMENT

Joints in floor slabs are unavoidable, they are required for the following reasons • As day joints, necessitated by the daily floor output restrictions.

• Accurately - levelled formed joints are required to enable flatness specifications to be met.

• To control shrinkage and warping stresses in the concrete.

• Differential vertical movement between adjacent bays of concrete results in joint arris breakdown.

• Lack of lateral dowel movement causes random cracking.

All joints need either dowel bars or tie bars through them to maintain load transfer and eliminate vertical movement. Even if contraction joints are provided at 6mm centres without reinforcement, shrinkage of up to 2mm can occur.

This is outside the limit at which “aggregate interlock” can provide load-transfer and consequently design safety factors have to be raised. Joints can be “tied” to reduce shrinkage to under 1mm at which it is accepted that load-transfer is maintained. Joints can be “tied” by using suitably anchored reinforcing steel.

A “tied” joint can only be used where contraction of the slab is allowed elsewhere, through the use of “contraction’ or “free-movement” joints (or perimeter isolation joints). Such joints must have reinforcement and must be debonded on one half to allow the slab to contract.

This is traditionally achieved through the use of round steel bar which is coated on one half with a debonding compound or debonded with a proprietary circular plastic sleeve.

Consider a common detail where a debonded induced transverse contraction joint crosses a long formed contraction joint at right angles. The true movement of the slab at the corner of the two joints, if it was free to do so, would be at 45 degrees, not 90 degrees, to either joint. The traditional round dowel, which has to be installed to provide load transfer, effectively constrains the slab at this point, completely defeating the object of the design.

Unexpected random shrinkage cracks then occur, the blame for which is usually attached to badly aligned dowels. In any event, the accurate alignment of round dowels is critical to their performance and almost impossible to achieve in practice.

All current joint details ignore any differential sideways movement (i.e parallel to the joint) which must occur whilst none of the recommendations for shrinkage control takes these additional stresses into account. Joints at right angles tend to lock a slab at the corners.

Norton dowel systems overcome all these problems by allowing two way lateral joint movement but no vertical movement between adjacent bays of concrete slab.

Diamond Dowel

Diamond Dowel

Viper Dowel

Supersleeve and Dowel Bar

Triplate

The information given is based on knowledge and performance of the material. Every precaution is taken in the manufacture of the product and the responsibility is limited to the quality of supplies, with no guarantee of results in the field as Norton Construction Products has no control over site conditions or execution of works.

CLF Concrete Laser Flooring Pty (Ltd)PO Box 2589, Witkoppen, Johannesburg, SA • www.concreteflooring.co.zaTel: +27 11 704 5557 • Fax: +27 11 462 1456 • E-mail: peter@concreteflooring.co.za